1. Field of the Invention
The present invention relates to a liquid crystal display module, and more particularly to a liquid crystal display module that can be illuminated with minimal light loss.
2. Description of the Related Art
Generally, a liquid crystal display module requires a separate light source because it is not a self-luminating device. Such liquid crystal display modules can be classified as a transmitting type and a reflective type in accordance with the type of light source used. The transmitting type of liquid crystal display module has a backlight unit facing a lower substrate of two substrates between which liquid crystal is injected, so as to transmit the light being incident from the backlight unit toward a plane of incidence. In contrast, the reflective type of liquid crystal display device has a specular surface formed on the lower substrate of two substrates between which liquid crystal is injected, so as to reflect the external light through the upper substrate to lower substrate toward a display surface.
The reflective type of liquid crystal display module realizes a picture using an external light, thus it is restricted from being used in a dark place. Therefore, the reflective type of liquid crystal display module with a front light unit is suggested.
FIG. 1 is a sectional view illustrating a reflective type of liquid crystal display module.
Referring to FIG. 1, the reflective type of liquid crystal display module includes a front light unit FL and a liquid crystal display panel LP located on the front light unit FL.
The front light unit FL includes a lamp 14 generating light, a lamp housing 4 equipped with the lamp 14, a light guide panel 2 to convert the light coming from the lamp 14 into a surface light and optical sheets having a diffusion sheet, and a phase difference compensation sheet and a polarizing sheet 18 which are fixed to the outgoing surface of the light guide panel in order to increase the efficiency of the light incident to the liquid crystal display panel LP.
The lamp 14 can be a cold cathode fluorescent lamp. And the light generated at the lamp 14 is incident to the light guide panel 2 through the incident surface that is adjacent the light guide panel 2.
The lamp housing 4 has a reflective inner surface in the inner surface covering the lamp 14 to reflect the light from the lamp 14 to the incidence surface of the liquid guide panel 2.
The light guide panel 2 takes the incident light from the lamp 14 and converts it into surface light to illuminate a position located far away from the lamp 14. Such a light guide panel 2 is made to have its incident surface and outgoing surface be perpendicular to each other. The light guide panel 2 has a horizontal outgoing surface to increase the efficiency of light and a tilt rear surface facing the outgoing surface. Either a groove or protrusion pattern is formed on at least one of the rear surface and the outgoing surface.
The polarizing sheet 18 transmits a specific linear polarized light from the external light and intercepts other polarizing components. The phase difference compensation sheet 10 converts a specific linearly-polarized light, which is transmitted from the polarizing sheet 18, into a circularly-polarized light. The diffusion sheet 8 is formed between the phase difference compensation sheet 10 and the upper substrate 20 to diffuse the light going out through the outgoing surface of the light guide panel 2 to the whole area. In this way, the light generated at the front light unit FL is incident to the liquid crystal display panel LP.
The liquid crystal display panel LP has liquid crystal cells arranged between the upper and lower substrates 20 and 22 in active matrix and has a thin film transistor installed to switch video signals at each of the liquid crystal cells. The refractive index of each liquid crystal cell is changed in accordance with the video signal, thereby displaying a picture corresponding to the video signal. That is, the liquid crystal display panel LP has its liquid crystal driven by the voltage difference between a common electrode of the upper substrate 20 and the a pixel electrode of the lower substrate 22 so as to selectively transmit the light from the front light unit FL, thereby displaying the picture. That is, a reflective electrode 6 is formed on the lower substrate 22 of the liquid crystal display panel LP, the reflective electrode 6 reflects the external light transmitted through the upper substrate 20 and the liquid crystal 12 toward the upper substrate 20.
The liquid crystal display module should have a gap between the light guide panel 2 and the polarizing sheet 18, and also between the light guide panel 2 and a touch panel (not shown). Accordingly, there is a problem in that the liquid crystal display module becomes too thick. In order to solve this problem, active study of a liquid crystal display module in which the light guide panel 2 and the optical sheets 8, 10 and 18 are integrated has recently progressed.
As illustrated in FIG. 2, the liquid crystal display module in which the light guide panel and the optical sheets are integrated, the optical sheets 8, 10 and 18 are formed on the outgoing surface of the light guide panel 2, thereby reducing the thickness of the front light unit FL. However, there is a problem in that the light going out from the light guide panel 2 is lost when passing through the polarizing sheet 18, the phase difference compensation sheet 10 and the diffusion sheet 8. This is because a total reflection condition existing in the air between the light guide panel 2 and the optical sheets 8, 10 and 18 cannot be realized between the light guide panel 2 and other optical sheets 8, 10 and 18 affixed thereon. Further, there is a problem in that the light, which should progress within the light guide panel 2, is not reflected at the border between the light guide panel 2 and the polarizing sheet 18, thereby generating light loss.